The aim of somatosensory rehabilitation is to increase the quality of touch or even normalize the sensation of touch in the case of neuropathic pain due to peripheral nerve lesions. Because, when hypoesthesia decreases, neuropathic pain decreases. The assessment of partial hypoaesthesia (axonotmesis) is based on the concept of the largest cutaneous distribution of the nerve branch. The first phase is the mapping which outlines the hypoaesthetic territory - aesthesiography. The second phase is the regular and rigorous assessment of the quality of hypoesthesia in terms of pressure perception threshold. This is an important part of this rehabilitation.
Sometimes, the hypoaesthetic territory is masked by a patch of skin which is painful to touch and is therefore not accessible. Since 1979, this stimulus induced pain is to be called allodynia in medicine. The original definition comes from Merksey and Bogduk (1994) “pain due to a stimulus which does not normally provoke pain”. In such situations, while doing the diagnostic testing of axonal lesions at the first occupational or physical therapy session, the two point discrimination test is impossible, because it induces pain.“This conflict between hypersensitivity and hypoaesthesia is commonly seen in the clinical setting in patients with CRPS”.
The presence of mechanical allodynia, hinders other physical treatments. For the reason that, any contact on the hypersensitive territory, although it can be bearable in the moment, can induce several hours of a very painful post-effect or even several sleepless nights. This hypersensitivity to touch is induced by the peripheral nerve lesion of the large myelinated A-beta fibers.
In other words, after a peripheral nerve lesion, aberrant sprouting occurs in the dorsal horn which can explain that a non-noxious stimulus is perceived as being noxious. This is one of the explanatory models of the different mechanisms of central sensitization.